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TitleOrganic Chemistry Reactions Book
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Table of Contents
                            Title Page
Part A
Part B
Part C
Part D
Notes
Note to Student
Table of Contents
Index
Functional Group by Starting material
Functional Group by Product
Preface
                        
Document Text Contents
Page 1

Curved Arrow Press
Princeton, New Jersey

A Guided Inquiry Workbook
Easy to Follow Curved Arrows

Peter Wepplo

A Guide to
A Sampler to

Organic Chemistry Mechanisms

This sampler contains problems from all chapters. It uses topics common to organic
chemistry textbooks and no additional introduction is provided. Therefore, you should
recognize the subject matter and its similarity to your textbook.

In Part A, you simply need to add the curved arrows or predict the equilibrium for acid-
base reactions.

In Part B, you will need to add the intermediates or products as well as the curved arrows.

In Part C, you will need to write a complete mechanism. The problems are the same

You should return to Parts A or B to practice the mechanism.

Part D give a completed mechanism.

The Notes are not the complete notes for the sampler, they are simply representative of
notes that are present in A Guide to Organic Chemistry Mechanisms.

Page 2

Curved Arrow Press
Princeton, New Jersey

A Guided Inquiry Workbook
Easy to Follow Curved Arrows

Peter Wepplo

A Guide to
A Sampler to

Organic Chemistry Mechanisms

http://www.curvedarrowpress.com

Page 28

Part C - Page 3

Curved Arrow Press A Guide to Organic Chemistry Mechanisms©

3. An E2 elimination reaction of 2-bromo-2-methylbutane to give 2-methyl-2-butene, a Zaitsev product.

CH3
CH3

Br
CH3

OCH2CH3

HO CH2CH3 Br

CH3
CH3

CH3
71%

CH3
CH3

29%

NaOEt

EtOH

10. An E1cb elimination reaction of 3-chloro-3-methylcyclohexanone with t-butoxide to give 3-methyl-2-cyclohexenone. (See
Notes.)

t-BuO

t-BuHO

O

Cl
CH3

O

CH3
H

KO-t-Bu

Acetylene Formation
20. A synthesis of 3-hexyne from trans-3-hexene by bromination and two elimination reactions. (See Notes.)

Br2

Br H

HBr

H

Br

Et C C Et

NH2

NH3 Br

NH2

NH3 Br
syn

elimination
slow

Br2

NaNH2,
2 equiv.

NH3

5 — Electrophilic Addition to Alkenes and Alkynes
Addition of HX and H2O to Alkenes
1. Addition of hydrogen bromide to propene to give 2-bromopropane. (See Notes.)

C

H

CH2H3C

H Br

Br

C

H

CH3H3C

Br

C

H

CH3H3C

BrHBr

7. Addition of hydrogen bromide to 3-methyl-1-butene to give after rearrangement, 2-bromo-2-methylbutane. (See Notes.)

CH2

H Br

Br

H

CH3H3C

CH3

H

H3C
CH3

H

CH3

H

CH3
H3C

CH3
CH3

H3C

Br
Br

IIo carbocation IIIo carbocation
CH3

CH3

CH3

Br

55%

45%

HBr

Page 29

Curved Arrow Press A Guide to Organic Chemistry Mechanisms©

Part C - Page 4

10. Addition of hydrogen chloride to 2-methyl-1,3-butadiene (isoprene) to give, 3-chloro-3-methyl-1-butene, the kinetic product,
or 1-chloro-3-methyl-2-butene, the thermodynamic product. (See Notes.)



CH3

H2C
CH2

H Cl

Cl CH3

CH3
CH2

Cl
CH3

CH3 Cl

CH3

CH3
CH2

Cl
CH3

CH3
CH2

Cl

IIIo
HCl

15. Bromination of methylcyclohexene to give (1R,2R)- and (1S,2S)-2-bromo-1-methylcyclohexanol. (See Notes.)



CH3 Br Br
CH3

Br O H
H

CH3Br CH3
Br

O

H

H
O H

H

H3O+

CH3

Br
O

H

Br Step intermediate

Br2

H2O

21. Addition of bromine to ethynylcyclopentane to give (E)-(1,2-dibromovinyl)cyclopentane and (1,1,2,2-tetrabromoethyl)
cyclopentane. (See Notes.)

HCC
Br Br

Br

HCC

Br

HCC

Br

Br
Br

HCC

Br

6 — Rearrangement Reactions
Baeyer-Villiger Oxidation
1. Acid catalyzed Baeyer-Villiger oxidation of 2,2-dimethylcyclopentanone with peracetic acid. (See Notes.)

O

O

O
O

H

O
H

O
H

O

O
O

H

O
H

O

O
O

H

cont'd

O
H

O

O

O

H

O
O

H3O

H O
H

H

HO
H

cont'd

CH2Cl2

CH3COOH

O

H2O
(cat. H2SO4)

Page 55

Page xiii

Curved Arrow Press

Preface

About the Book

This book is a guide for learning organic chemistry reaction mechanisms. How should you use this book? Since I
believed that I could always adapt a reaction to a new problem, I just need to know at least one example. This book is
designed to teach that example. This book will help you to learn reactions in small portions making it easier for you to
understand and remember.

However, before you start with the reactions, there are some things you should review. Therefore, Chapters 1 and 2 go
over some fundamentals. In Chapter 1, I discuss some chemical principles that you can use to predict electron reactivity.
This is followed by resonance structures. The problems are designed to be easy and illustrate patterns. This should
appeal to our brains ability to fi nd patterns that we can repeat. Therefore, you should succeed in completing all of these
problems.

Resonance structures show how electrons move without forming any bonds to new atoms. In Chapter 2, you will do
acid-base reactions. You will learn how to predict the equilibrium of a reaction and you will learn how to use the curved
arrow. I have added an exercise to write English sentences with the curved arrows. I want to connect the logic of a
curved arrow to a sentence as well as the graphical representation.

Now, start with any of the reactions or chapters and start with the Part A problems. Fill in the missing curved arrows.
Everything you need to know is present in Part A. This shows the logic of a reaction. You must write the correct
curved arrows for each step before you go to Part B. Go to that same reaction in Part B and repeat that reaction. Now
you must add any missing ‘pre-bonds’, curved arrows, and structures. While I have removed some information from
the reaction, the basic logic of the reaction remains. Finally, complete Part C. This is similar to problems in an organic
chemistry textbook. I have retained the same number of reaction arrows as the original mechanism as additional hints.
In addition, the reagents are written with their complete formulae and solvents are added but noted in italic type. You
should strive to write out the complete mechanism. You may wish to photocopy a reaction or write it on a blank sheet
of paper so you can go back and repeat an exercise. Once you have succeeded in writing a mechanism, you can move
on to problems from your text.

The reactions are grouped by reaction type because it is easier to learn a series of related reactions. If your book is not
organized in that manner, then select similar examples from the table of contents or from the index.

If you are able to write a mechanism for a problem in this book, you should be able to write a mechanism for other
problems of the same mechanism. You should use this approach to solve the problems in your textbook. Clearly, you
must be able to solve at least one problem if you are to solve another problem using that same mechanism.

You objective in studying should be to learn the patterns of the reaction mechanisms. The fi rst problem always takes
the greatest amount of time because you must learn the most to solve it. The more problems you solve, the less time it
will take to solve them.

Writing Style (and Meaning)

I also wrote this book in the fi rst person. Why write in the fi rst person? First of all, it is a format that I am comfortable
with. I like how it sounds. I also want to write in the fi rst person because science can be gray. A scientifi c proof may
not be as strong as we would like it to be. I think we are too frequently willing to accept something as true simply
because it is written in a book. By writing in the fi rst person, you will have a natural sense that an idea is my idea and
other scientists may not accept it. As some of the mechanisms, topics and models contained in this text are different; I

Page 56

A Guide to Organic Chemistry Mechanisms©

Page xiv

will leave it to you to determine whether they are useful or true.* I hope by doing so, you may go back to your regular
textbook and measure the thoughts of that author in the same manner. †

The Curved Arrow

The ‘curved arrow’ is the symbol that represents how electrons move. They indicate which bonds are being made and
broken AND which atoms are being joined. They are the language of organic chemistry and their use is also referred to
as ‘pushing electrons’.

In this book, I use a simple modifi cation of pushing electrons. The traditional curved arrows are ambiguous if the
curved arrow starts with a pair of electrons shared by two atoms AND indicate indicate a new bond being formed. This
ambiguity can be avoided if a curved arrow does not indicate formation of a new bond. Therefore, a “pre-bond” or
dashed line has been added to indicate where new bonds will be formed. It is used with the curved arrow to show which
electrons move to make or break bonds and makes pushing electrons consistent and unequivocal in meaning.‡

Curved arrows are fundamental to understanding chemistry. The curved arrows are a required element in describing
what is happening in a reaction. They describe the only electronic changes that can be made in any step in a reaction. If
there is a curved arrow, that change must be made, and unless there is another curved arrow, no other changes can be
made. Here is where students make a very common error. A student may write a curved arrow believed to lead to the
formation of a product. However, the product they write will not be consistent with the curved arrows. Any difference
between a curved arrow and the predicted result is an error of critical importance.

Another error is to fail to start the curved arrow with a pair of electrons. Some students may start a curved arrow at a
proton to show its movement. However, the curved arrow represents a movement of electrons, not protons. A useful
device I often use and encourage students to use, especially initially, is to circle the electrons being moved.

Rules for Pushing Electrons

To Make a Bond or Increase the Bond Order
Two Electrons One Electron

A curved arrow must start with a pair of electrons on an atom or
connecting two atoms and end between two atoms. It may point
toward a pre-bond to indicate a new bond or to a single, or a double
bond for a change in bond order. A bond will form to the common
atom of the starting material and product.

Two half-headed curved arrows must end between two atoms
and point toward a pre-bond, single, or double bond to indicate
a new bond or a change in bond order. Each atom donating an
electron are part of the new bond.

To Break a Bond or Reduce the Bond Order
Two Electrons One Electron

A curved arrow must start with a pair of electrons connecting two
atoms. That bond will be broken or reduced in bond order. If a curved
arrow ends between two different atoms, a new bond is formed to the
common atom. If not, no new bond is formed.

Two half-headed curved arrow must start with a pair of electrons
connecting two atoms. That bond will be broken or reduced in
bond order. The curved arrows may end on an atom or connect
to new atoms to form new bonds..

A Guide to Organic Chemistry Mechanisms© Peter Wepplo, 2008

* What is the difference? Models are never true, but they can be useful. If a model were true, then it wouldn’t be a model for something.
† Ideas presented in peer-reviewed journals will contain a reference to their source. Therefore, a reader understands that the idea belongs to the

source. If authors accept the principles fi rst laid out, then they may become commonly accepted. However, in the strictest use of logic, it does
not become more true. It will remain only as true as the original proof or proofs.

‡ Many books use this convention, especially with Diels-Alder reactions. I have added the term ‘pre-bond.

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